[ARC5] ARC-5 on 20 meters

[Dave Merrill]

On Thu, Dec 29, 2016 at 12:49 PM MICHAEL ST ANGELO <mstangelo at comcast.net>
wrote:

> I searched for ARC-5 in the QST archive and found an article in the June
> 1948 issues of QST "ARC-5 Transmitter Modifications".
>
>
> Even though the title says ARC-5 the article discusses two ways to modify
> the BC-459-A for 14 MHZ (or as they said back then 14-Mc.).
>
>
> Both methods involve modifying the output to a PA doubler.
>
>
> The first  mod is simple but you lose the PA and Oscillator condenser
> (capacitor) tracking. remove the C67 padding cap and C65 PA tuning cap from
> the circuit and replacing with a 75 uufd (pF) variable.
>
>
> The second mod preserves tracking and improves doubling efficiency.
>
>
> - Remove the C67 padding condenser and replace with a 35uufd variable.
>
> - Remove 10 rotor plates from the PA tuning condenser.
>
> - The plate coil is pruned down to 5 1/2 turns.
>
>
> Plate-circuit tracking is adjusted with the new variable and by
> positioning the top turn on the coil.
>
>
> To increase the doubling efficiency
>
>
> - The tap of the grid leak R74 and grid leak bypass condenser C58 is
> moved  to the bottom of the grid coil.
>
> - The  value of the grid leak bypass condenser is changed from 0.05 ufd to
> 0.00025 ufd.
>
> - Remove the fixed neutralizing condenser C62.
>
>
> Mike N2MS
>

The 1949 edition of *Hints & Kinks* has three articles on modifying
SCR-274N transmitters for 20 meters.  The first, written by William Orr
W6SAI, uses a 6AG7 doubler feeding a single 1625 configured as a doubler on
20 or an amplifier on 40.  He starts with either a BC-457-A or a BC-696-A,
very extensively modified.  This article is too big to attach due to
reflector size restrictions.

The other two articles by W8ZGO and W1DX are attached.  They both modify a
BC-459-A.

73 Dave N9ZC
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